The present invention relates to a pump casing made of sheet metal, and more particularly to a pump casing made of sheet metal which has a sufficient strength and rigidity against external forces such as piping forces which are applied to a suction flange and an outlet flange provided on the pump casing.
Conventionally, there is known a pump casing made of sheet metal in which a casing jacket is formed of sheet metal such as a stainless steel and manufactured by press work. As shown in FIG. 13(a) and (b), this type of pump casing is provided with a suction nozzle 4 having an end to which a suction flange 14 is integrally attached. The pump casing also includes an outlet nozzle 22 having an end to which an outlet flange 23 is integrally attached. Further, the pump casing is integrally formed, at the side of a motor, with a casing flange 2 which is attached to a bracket 5 made of castings. A casing jacket cover 12 is attached to the casing flange 2 in such a manner that the outer periphery of the casing jacket cover 12 is engaged with the casing flange 2 and fixed to the casing flange 2. An impeller 8 is housed in the inside of the casing jacket 1 and the casing Jacket cover 12, and is supported by the end of a shaft 10 connected to a motor M. A shaft seal 11 such as a mechanical seal is provided between the casing jacket cover 12 and the shaft 10 to seal off the clearance therebetween. The casing jacket 1 is fixedly mounted on a base 24 through a leg member 13.
The above conventional pump casing is formed of a relatively thin plate because it is restricted by the characteristics of press work and by manufacturing costs. Therefore, not only an internal pressure generated by the pump per se but also external forces such as piping forces are applied to the pump casing, thus causing the pump casing to be deformed.
Therefore, conventionally, as shown in FIGS. 13(a) and 13(b), in order to cope with the piping forces applied to the suction flange, supporting members 19 are provided between the suction flange 14 and the casing jacket 1. Although the piping forces are transmitted to the casing jacket 1 through the supporting members 19, the casing jacket 1 inherently does not have a sufficient strength to bear the piping forces. As a result, the casing jacket 1 is deformed, the liner portion 1L integrally provided on the casing jacket 1 may be slightly brought into contact with an end portion 8a of an impeller 8. This slight contact generates noise and causes overload. It further tends to lead to closer contact of both members (the liner ring portion 1L and the end portion 8a of the impeller 8) which causes unexpected trouble such as damage to the impeller.
On the other hand, in order to cope with the piping forces applied to the outlet flange 23, similar supporting members 40 are provided between the outlet flange 23 and the casing jacket 1. However, as mentioned above, the casing jacket 1 does not have a sufficient strength to bear the piping forces.
Further, as shown in FIG. 13(b), since the end plate 7 is axially inwardly curved, the end plate 7 is deformed by internal pressure to thereby bulge axially outwardly. Thus, a great deal of bending stress is generated at the connecting portion of the casing cylindrical portion and the end plate 7. In the type of casing having a projecting portion radially outwardly bulged to form a volute shape, in general, since a bent portion is formed at the connecting portion of the casing cylindrical portion and the projecting portion, a great deal of bending stress is generated by the internal pressure at the bent portion. That is, the conventional casing does not have sufficient strength to withstand the piping forces as well as the internal pressure.